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This web site shows the results from one of the work packages (WP1: RF Spectral Survey) undertaken as part of a UK Government-funded pilot project on 'Ambient RF Energy Harvesting'. This work was also partially funded by the Mexican National Council of Science and Technology (CONACYT).

In order to identify RF power density levels suitable for ambient harvesting within an (semi-)urban environment, a city-wide RF spectral survey was conducted within greater London.

In order to provide a robust data set of measurements across greater London, in terms of geographical distribution and population density (with the centre having a truly urban environment and the surrounding areas being semi-urban), while also providing a convenient means of transportation between locations, London Underground was used. Here, field measurements were taken at each of the 270 underground stations (at street level from one of the exits). To provide some degree of traceability, time stamps and GPS locations were recorded.

In summary, while digital television (DTV), GSM900, GSM1800, 3G and WiFi have been identified as potentially useful RF energy sources, DTV appears to be heavily dependent on atmospheric conditions; while Wi-Fi is dependent on user traffic. With the former, it is important to note that the spectral measurements were undertaken during the analogue-to-digital switchover period, and so the measurements for DTV may represent an underestimate of power levels measured today.

It is hoped that the information represented in this web site will serve as a snapshot of London’s RF spectrum that can be used as a historical reference for future surveys.

Measurement Methodology

Spectral measurements were taken from 10:00 am to 3:00 pm during weekdays, between the 5th March and 4th April 2012. Electric field strength was measured between 0.3 and 2.5 GHz, using the Agilent N9912A FieldFox RF Analyser and a calibrated Aaronia BicoLOG® 20300 omnidirectional antenna. The 'paning method' was used to cover orthogonal antenna polarizations. With this standard technique, the calibrated antenna is rotated to cover all three orthogonal axes while the spectrum analyser is set to 'max-hold', to ensure that the maximum reading is recorded. To maintain a comparable signal to noise (S/N) ratio, attenuation was introduced (with a minimum set at 5 dB), to avoid compression when high input power levels were detected. Finally, with all measurements, the internal amplifier was set to ON, the highest resolution of 1001 points was selected and the resolution bandwidth was fixed at 100 kHz.

Imperial College Team Members (from left to right)

Dr Paul D. Mitcheson, Chen Wang, Fangjing Hu, Manuel Pinuela (above), Dr Stepan Lucyszyn (below), Stergios Papantonis, Alwyn Elliot, Elpida Episkopou, Mario D’Auria, Shuo Yang... and not shown James Dicken (web page developer)